1. Field of the Invention
The invention relates to a vibratory compactor used, e.g., to compact backfilled trenches after a pipeline is laid or to compact the floor of a trench prior to laying a pipeline and, more particularly, relates to a vibratory compactor of the above-mentioned type and having an easy to assemble, low inertia to compact exciter assembly. The invention additionally relates to an exciter assembly usable in a vibratory compactor and to a method of assembling the exciter assembly.
2. Discussion of the Related Art
Vibratory compactors are used in a variety of ground compaction and ground leveling applications. Most vibratory compactors have plates or rollers that rest on the surface to be compacted and that are excited to vibrate so as to compact and level the worked surface. A common vibratory compactor, and one to which the invention is well-suited, is a vibratory trench roller.
The typical vibratory trench roller includes a chassis supported on the surface to be compacted by one or more rotating drum assemblies. Two drum assemblies are typically provided, each of which supports a respective subframe of the chassis. The subframes are articulated to one another by a pivot connection. Each of the drum assemblies includes a stationary axle housing and a drum that is mounted on the axle housing and that is driven to rotate by a dedicated hydraulic motor. All of the hydraulic motors are supplied with pressurized hydraulic fluid from a pump powered by an internal combustion engine mounted on one of the subframes. In addition, each drum is excited to vibrate by a dedicated exciter assembly that is located within the associated axle housing and that is powered by a hydraulic motor connected to the pump. The exciter assembly typically comprises one or more eccentric masses mounted on a rotatable shaft positioned within the axle housing. Rotation of the eccentric shaft imparts vibrations to the axle housing and to the remainder of the drum assembly. The entire machine is configured to be as narrow as possible so as to permit the machine to fit within a trench whose floor is to compacted. Machine widths of under 3 feet are common. Vibratory trench rollers of this basic type are disclosed, e.g., in U.S. Pat. Nos. 4,732,507 to Artzberger and 5,082,396 to Polacek.
Many vibratory trench rollers and some other vibratory compactors require that the amplitude of the vibrations generated by the machine's exciter assembly be varied. For instance, it is often desirable to generate relatively low amplitude vibrations during machine start and stop operations to reduce the likelihood of disturbing the freshly compacted surface and to otherwise generate higher amplitude vibrations to maximize compaction. To achieve this effect, many vibratory trench rollers incorporate a so-called “dual amplitude exciter.” A dual amplitude exciter typically has multiple eccentric weights mounted on its rotatable shaft. A first, relatively massive eccentric weight is fixed to the shaft so as to rotate with it. One or more additional, less massive eccentric weights are mounted on the shaft so as to be swingable on it between at least two angular positions. Each of these “free swinging” weights has a tab or other structure that limits the range of rotation relative to the fixed weight when the exciter shaft rotates in a particular direction. When the exciter shaft is driven in a first direction, each free swinging weight swings to a first angular position on the exciter shaft in which its eccentricity adds to the eccentricity of the fixed weight, generating high amplitude vibrations. Conversely, when the exciter shaft is rotated in the opposite direction, each free swinging weight swings to a second angular position on the exciter shaft in which its eccentricity detracts from the eccentricity of the fixed weight, thereby generating low amplitude vibrations. Dual amplitude exciters are disclosed, e.g., in U.S. Pat. No. 4,830,534 to Schmelzer et al. and U.S. Pat. No. 5,618,133 to Mitsui et al.
The typical dual amplitude exciter, though adequately generating both high and low amplitude vibrations, exhibits several drawbacks and disadvantages. First, it is relatively complicated and difficult to assemble. The free swinging weights are mounted on the exciter shaft using relatively complex ring retainers that positively couple the weights to the exciter shaft so as to permit them to rotate between their first and second positions on the exciter shaft while restraining them from substantial axial movement along the exciter shaft. These retainers substantially increase the overall complexity of the exciter, hindering assembly of the machine and increasing the exciter's cost. Assembly is further hindered by the need to assemble at least part of the exciter within the drum assembly rather than as a separate subassembly that can be inserted into the axle housing as a unit. The extra hardware required to mount the free swinging weights and other components of the exciter on the exciter shaft and/or to mount the exciter in the axle housing also substantially increases the weight of the exciter, thereby increasing its inertia. The relatively high inertia undesirably increases exciter startup time.
Another problem associated with traditional exciter designs is that they are too lengthy to receive a coaxial motor when they are used on a vibratory trench roller. That is, the mounting hardware for the free weights, bearings, and other components of the exciter substantially increases the overall length of the exciter beyond that which would permit it to be mounted within an axle housing of standard length. Providing a longer axle housing is not an option because the permissible length of the axle housing is restricted by the width of the overall machine, which must be narrow enough to permit the trench roller to be placed inside a trench. As a result, it has heretofore been necessary to mount the exciter drive motor non-coaxially with the exciter drive shaft and to couple to the output shaft of the exciter drive motor to the exciter drive shaft via a gear train or similar torque transfer system. This requirement significantly increases the overall weight and complexity of the machine. It also hinders access to hydraulic hoses and connections for the exciter drive motor, hindering motor repair and maintenance.
The need therefore has arisen to provide an exciter assembly for a vibratory roller or the like that is relatively lightweight and easy to assemble.
The need has also arisen to provide an exciter assembly for a vibratory trench roller or the like that is as short as possible.
The need has additionally arisen to provide a vibratory roller that has improved startup capability and that requires less exciter drive torque than traditional vibratory rollers.